1. Field of the Invention
The present invention relates to a method for the oxidation of at least one alkaline metal, according to which this alkaline metal in molten condition is subjected to an oxidation by reaction with oxygen.
2. Discussion of the Related Art
The alkaline metal can be radioactive as well as non-radioactive.
The radioactive alkaline metals substantially are results of nuclear experiments, whereby they either have been brought into contact with radioactive isotopes or have been subjected to a neutronic flow, so that an activation was effected.
Generally, large quantities of alkaline metals are difficult to store for a longer period of time, as a result of the large reactivity which this metals show in respect to water and oxygen. Said reactions are extremely violent and carry along the risk of explosion as a result of the production of hydrogen in the case of reaction with water, or peroxides in the case of reactions with oxygen. Also, fires which cannot be controlled by classic means, as water is to be excluded, may occur. Moreover, the very exothermic character of this reactions even enhances the risks of an accident by explosion or fire.
Large quantities of such metals exist, however, particularly in the nuclear branch, where, for example, liquid sodium is used as a cooling fluid. The question of safe and efficient treatment of these metals, whether they are radioactive or not, is acute.
In fact, there exist various methods of treatment, but none guarantees a satisfactory level of total security, and none suggests a solution which is perfectly compatible to the necessary conditioning after treating, whereby this latter point is particularly crucial in the case of contaminated alkaline metals.
As the oxidation of alkali metals creates serious safety problems when an oxidant is used which contains hydrogen, such as water or alcohol, or an oxidant which is susceptible to combustion, such as alcohol, it is preferable to apply an oxidant which does not contain hydrogen and which is not combustible itself, in other words, oxygen.
Such a method is described in U.S. Pat. Nos. 1,685,520 and 2,825,629. This method is based upon the calcination of the metal by reaction with oxygen or air. It shows, however, the disadvantage that it does not oxidize the metal completely, as minor quantities of the latter do not react, due to the protection by oxidation on the surface, what maintains the aforementioned risks. The calcination also shows the risk of leading to the formation of peroxide which is known as unstable and which is also susceptible to provoking explosions.
The treatment of alkali metals according to the said method generally results indirectly in the production of hydroxides in aquaeous solution after hydration of the oxides and peroxides. Moreover, the same hydroxides are formed directly when the oxidation is performed with water, or indirectly after hydrolisis of the ethyl alcohol in case of an oxidation with alcohol.
Whether the metals are radioactive or not, these hydroxides necessitate an additional treatment due to their corrosive character. This question is particularly acute in the case of treatment of radioactive metals, for which it is necessary to provide in a definitive conditioning which offers the prospect of a long-term storage.